| Luminance was changed at one log unit per twenty-two minutes in three stimulus conditions (normal image, no image, a single edge scene in which the luminance change modifies the edge ratio). The presence or absence of an image has no effect on detection of slow luminance change. Detection of a slowly changing edge ratio occurs much sooner, although observers detect the contrast change without being aware of which region has changed. A change in the local edge is more likeley to be interpreted as change in a surrounded region than change in the surrounding region. The visual system is most sensitive to small changes in the local edge ratio when the edge contrast is low. |
